Internal combustion engines for tractors and similar vehicles may include an throttle position sensor to provide electronic information about the position of the throttle to an electronic controller. The throttle position sensor may include a potentiometer that provides an output signal of a varying voltage. For example, a potentiometer may provide a voltage with a value of about 0.6 volts to about 1.2 volts for the lowest engine speed (typically about 950 rpm), and a value of about 3.6 volts to about 4.4 volts for the highest engine speed (typically about 2750 rpm). The electronic controller may have a calibration routine to determine the actual low and high engine speed throttle position voltage for each tractor and/or engine.
The calibrated voltages may then be used to map the throttle position sensor output voltage into a predicted engine speed. For example, the low engine speed calibrated voltage may map into a predicted engine speed of about 950 rpm, the high engine speed calibrated voltage may map into a predicted engine speed of about 2750 rpm, and voltages between the low and high engine speed calibrated voltages may map into engine speeds according to the mathematical rules of a mapping algorithm in the controller software.
The mapped engine speed that the throttle position sensor voltage signal provides to the controller may be used as a predicted engine speed. The controller may compare the predicted engine speed to the actual engine speed. If the actual engine speed is less than the predicted engine speed, for example, the controller may provide input to a hydrostatic transmission to reduce the output to the hydrostatic transmission swash plate position control pressure reducing proportional valve coil to command the hydrostatic pump to do less work and thereby attempt to bring the actual engine speed back up to the predicted engine speed. This action is typically referred to as an anti-stall feature.
The throttle position sensor output also may be a pulse width modulated output that varies based on rotary position. Alternatively, the rotary sensor may shape its output in such a manner relative to rotary position to duplicate or provide a similar effect of the controller mapping algorithm.
The throttle position sensor typically may be mechanically biased to a high voltage position. However, during assembly, the throttle position sensor must be preloaded to a low voltage position to represent a low idle. A voltage meter or similar calibration device may be used to determine if the throttle position sensor is at a voltage within a specified range. If the engine is at a low idle position, linkages from the throttle are connected such that the throttle position sensor will be in the low voltage position. If the engine is at a higher speed position (for example, high idle), linkages from the throttle are connected so that the throttle position sensor will be set at a higher voltage position. The throttle position sensor also may be calibrated for other engine speeds.
During assembly, adjustments to the throttle position sensor and/or linkages may be required to make sure that the throttle position sensor provides a voltage within a specified range for the predicted engine speed. It is difficult and takes time intensive to do this. A throttle position sensor and linkage is needed that will reduce the difficulty and time for calibration at one or more specified engine speeds.
Additionally, there may be a tolerance stack-up of parts and/or linkages that are assembled between the engine throttle and the throttle position sensor. Because of the tolerance stack-up, the throttle position sensor may need to be set slightly differently on each tractor or other vehicle. A throttle position sensor and linkage is needed to help reduce or minimize the tolerance stack-up problem and inconsistency of voltage settings from tractor to tractor.
Linkages and parts that connect the throttle to the throttle position sensor also may be subject to wear over time. This can lead to the throttle position sensor providing a voltage value that falls outside the specified range for a specified engine speed, reducing engine performance and requiring adjustment and recalibration. A throttle position sensor and linkage is needed that will provide a more consistent voltage setting regardless of wear and tear to the linkage, and that will maintain optimum engine performance and reduce or eliminate the need for adjustment and/or recalibration.